To attain a desired flexibility regarding coverage and/or frequency bandwidth in advanced communication systems or sensor systems such as a radar, large array antennas with controllable beamforming are required. Array antennas with a large number of antenna elements, irrespective of whether an analogue or digital beamforming is involved, will require an unwieldy amount of information transfer as each antenna element has to deliver its values to a beamformer. To enable flexibility and a reasonable cost efficiency, practically all beamforming today is done by means of digital signal processing.
Array antenna systems with digital beamforming used today are typically of high complexity resulting in high costs and high power consumption. A first example is a system where each antenna element feeds its radio frequency (RF) signal to a centralized beamformer that performs analogue to digital (A/D) conversion and the subsequent digital signal processing. A system according to this first example will quickly result in an unwieldy large RF coupling network as the number of antenna elements rise. Such a system would also require a very advanced signal processor.
In a second example each antenna element performs any necessary analogue preprocessing and the A/D conversion. Digital signal values from each antenna element will then have to be either directly connected with a central digital beamformer resulting in a very large number of cables and connectors, or be connected to the central digital beamformer by means of a digital data bus, which would require a very wide high-capacity data-bus, which would be very expensive. A system according to the second example would also require a very advanced central signal processor to calculate the desired beam or beams.
A third example is a hybrid system with both digital and analogue beamforming. The array antenna is divided into subunits, where each subunit comprises a more manageable number of antenna elements. The antenna elements of each subunit are beamformed together in an analogue manner before being A/D converted and transferred to a central digital beamforming unit. The third example is often considered a good compromise, but it does not give all of the advantages of digital beamforming. There would thus seem to be room for further improvement in the area of digital beamforming in array antennas with a large number of antenna elements.